Cylindrical drum



March 1969 J. VAN DER HILST 3,

CYLINDRICAL DRUM Filed June 27, 1966 FIG.1

INVENTOR. JAN VAN DER HILST AGENT United States Patent 3,431,617 CYLINDRICAL DRUM Jan van der Hilst, Eindhoven, Netherlands, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed June 27, 1966, Ser. No. 560,726 Claims priority, application Netherlands, July 22, 1965,

6509476 US. Cl. 29-123 3 Claims Int. Cl. B21b 27/00 ABSTRACT OF THE DISCLOSURE This invention relates to cylindrical drums of the type which is provided with a base plate at or near at least one extremity and which is rotatable about its own axis. In such a cylindrical drum it is known to secure the base plate directly and rigidly to the drum.

If the drum is rotating at high velocities about its own axis the rigid connection, due to the radial expansion of the base plate being considerably less than that of the wall of the drum, will influence the action of the centrifugal forces on the wall of the drum so that the drum assumes the bulging shape of a barrel which differs from the cylindrical shape. If such a cylindrical drum is used as a quick-rotating memory drum for magnetic recordings, the barrel-shaped deformation of the periphery of the cylinder will result in intolerable variations in the width of the gap between the surface of the drum and the memory head.

An object of the invention is to provide a fastening construction between the drum and the base plate, which is such that the wall of the drum can expand freely in the radial direction throughout its length and hence the cylindrical shape is retained at any arbitrary, even very high rotational speed of the "drum.

According to the invention, to this end, a cylindrical drum of the kind mentioned above is characterised in that the drum is secured to the base plate by means of a hollow auxiliary cylinder the extremities of which are connected to the wall of the drum and the base plate, respectively, the length L, the mean radius R and the wall thickness t of the auxiliary cylinder being chosen to s be such that whilst the material and the dimensions of the auxiliary cylinder are such that for the drum and the cylinder the expression pR /E is the same or approximately the same, where:

p=specific mass of the material,

R= mean radius (half the sum of the external and internal radii),

E=elasticity modulus of the material.

Since, in the drum according to the invention, the length L of the auxiliary cylinder is equal to L 2.5 /Rt the cylinder may be regarded with respect to radialsymmetrical deformation as infinitely long, that is to say the radial expansion occurring at the extremity which is connected to the base plate has no influence on 3,431,617 Patented Mar. 11, 1969 'ice the radial expansion of the other extremity which is connected to the drum. Since, furthermore, the expression pR /E is approximately the same for the drum and the cylinder, the radial expansions of the end of the cylinder which is connected to the drum and the wall of the drum will be substantially the same, which implies that the wall of the drum can expand substantially freely, not being hindered by the fastening of the cylinder at the base plate, throughout its length, so that the cylindrical shape is substantially retained.

A suitable embodiment of the invention consists in that the auxiliary cylinder lies within the drum and is made of similar material to that of the drum, the auxiliary cylinder having an external diameter and a wall so thin in proportion to the wall thickness of the drum, that the mean radius of the auxiliary cylinder approximates as far as possible that of the drum.

The advantage of the embodiment consists in that the total length of the drum construction is minimized, which is important, for example, for memory drums in which a maximum number of recordings per unit structural volume is aimed at.

Another suitable embodiment of the invention consists in that an annular groove concentric with the axis of the drum is formed in the wall of the drum at the extremity engaging the base plate and extends inwardly through part of the length of the drum. By so dividing the Wall of the drum into an outer cylinder and an inner cylinder, the inner cylinder constituting the auxiliary cylinder is formed.

In addition to the advantage of a compact structural length which is obtained in the embodiment previously described, the last-mentioned embodiment has the further advantage that it is possible to make the mean radii of the drum and of the auxiliary cylinder more nearly equal to each other so that, upon expansion of the wall of the drum during high speed rotation, the cylindrical shape is retained with more accurate approximation.

In order that the invention may be readily carried into effect, several embodiments thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 shows a longitudinal section of one end part of a drum according to the invention, and

FIG. 2 shows a longitudinal section of a modification of one end of the drum.

FIG. 1 shows part of a cylindrical drum 1 which is secured, at least at one end, to a base plate 2 through the intermediary of a hollow auxiliary cylinder 3 placed in the drum and having ends 4 and S which are connected, for example by welding, to the drum 1 and the base plate 2 respectively. The drum 1 is supported to rotate about its own axis in a manner not shown.

The dimensions of the auxiliary cylinder 3 are chosen to be such that LE2.5 /Rt where L is the length, R is the mean radius (half the sum of the external and internal radii), and t is the wall thickness of the cylinder 3. If this relationship is fulfilled, the auxiliary cylinder may be considered with regard to radial-symmetrical deformation as infinitely long, which means that radial deformation occurring at one end of the cylinder does not result in radial displacements of points at the other end of the cylinder.

In the embodiment shown, the auxiliary cylinder 3 is made of a material similar to that of the drum 1. The cylinder 3 is placed at a substantial fit in the drum and has a wall which is thin in proportion to the wall thickness of the drum, in order that the mean radius of the cylinder approximates to that of the drum as far as possible. Consequently the expression pR /E for the drum and the cylinder and hence the radial expansions of the ends 4 of the 3 cylinder and the associated ends of the drum are substantially the same. In fact, the expansion of the end of the drum is not influenced by the attachment at the end 5 since the cylinder 3 may be regarded as infinitely long.

Preferably an exact fit between the drum and the cylinder exists at least at the base plate 2 in order to permit the drum, supported by the cylinder and the base plate, to be machined, for example turned off, at its outer periphery, the base plate being able to absorb via the cylinder the radial forces which occur during this process. This fit intended for machining will undo during the quick rotation of the drum.

In the embodiment shown in FIG. 2 an annular groove 7 is formed at that end of the drum 9 provided with the base plate which is formed by a wall part of the drum. The groove 7 divides the wall of the drum into an outer cylinder and an inner cylinder 6', the inner cylinder 6' constituting the auxiliary cylinder. The groove 7 has a width and a depth such that the auxiliary cylinder 6' may again be regarded as infinitely long. In this embodiment the mean radii of the drum 9 and the cylinder 6' may more nearly approximate to each other than in the embodiment of FIG. 1, so that the cylindrical shape of the drum during rotation of the drum may be retained with even more accurate approximation.

The base plate 10 to which the free end 11 of the cylinder 6 is secured, for example by gluing, is placed as a close fit in the end of the drum in order to permit the drum supported by the base plate, to be machined at its outer periphery.

It should be noted that the invention is not limited to quick-rotating memory drums but also applicable to fastrotating cylindrical drums in general which have to satisfy the condition of maintaining their cylindrical shape during high-speed rotation.

What is claimed is:

1. A rotatable drum comprising a cylindrical body portion rotatable about the central axis thereof, a base plate member arranged at one end of said cylindrical body portion and having a central axis coincident with the axis of said cylindrical body portion, and means interconnecting said base plate and the cylindrical body portion, said means comprising an auxiliary cylindrical member having one end secured to the cylindrical body portion at an end portion thereof and having the other end thereof secured to said base plate at a peripheral portion thereof, said auxiliary cylindrical member having an effective length L 2.5 /R t and a characteristic p R /E approximating the characteristic p R /E of the cylindrical body portion wherein R and R represent respectively the mean radius of the auxiliary cylindrical member and of the cylindrical body portion, t is the wall thickness of the auxiliary cylindrical member, p and p represent respectively the specific mass of the auxiliary cylindrical body and of the cylindrical body portion, and E and E represent respectively the elasticity modulus of the auxiliary cylindrical body and of the cylindrical body portion.

2. A rotatable drum as claimed in claim 1 wherein said auxiliary cylindrical member consists of a material similar to that of the cylindrical body portion, and is in the form of a sleeve having a mean radius substantially equal to the mean radius of the cylindrical body portion.

3. A rotatable drum as claimed in claim 1 wherein said cylindrical body portion is provided with an annular groove at the extremity thereof, wherein said cylindrical member is an integral sleeve formed by said groove, and wherein said base plate is secured to the free end of said sleeve.

References Cited UNITED STATES PATENTS 3,097,590 7/1963 Justus -155 3,138,089 6/1964 Shelton 29-129 X 3,138,848 6/1964 Cheney 29123 BILLY J. WILHITE, Primary Examiner.

US. Cl. X.R. 29-129, 346-138 

